Today I got a message in the alert log which is new to me:
Thread 1 cannot allocate new log, sequence 607
Private strand flush not complete
Private strand flush not complete… sounds similar to checkpoint not complete. So the next step brought me to Metalink and there I found note 372557.1.
What you can read in there is that Oracle hasn’t completed writing all the redo information to the log at the logfile switch. It is also written that this is similar to a “checkpoint not complete” except that this only involves the redo being written to the log and that the log switch can not occur until all of the redo has been written.
The next thing: What’s a private strand?
A “strand” is new terminology for 10g and it deals with latches for redo.
Strands are a mechanism to allow multiple allocation latches for processes to write redo more efficiently in the redo buffer and is related to the log_parallelism parameter present in 9i.
The concept of a strand is to ensure that the redo generation rate for an instance is optimal and that when there is some kind of redo contention then the number of strands is dynamically adjusted to compensate.
The initial allocation for the number of strands depends on the number of CPU’s and is started with 2 strands with one strand for active redo generation.
For large scale enterprise systems the amount of redo generation is large and hence these strands are *made active* as and when the foregrounds encounter this redo contention (allocated latch related contention) when this concept of dynamic strands comes into play.
There is always shared strands and a number of private strands .
Oracle 10g has some major changes in the mechanisms for redo (and undo), which seem to be aimed at reducing contention.
Instead of redo being recorded in real time, it can be recorded ‘privately’ and pumped into the redo log buffer on commit.
Similary the undo can be generated as ‘in memory undo’ and applied in bulk.
This affect the memory used for redo management and the possibility to flush it in pieces.
The message you get is related to internal Cache Redo File management.
You can disregard these messages as normal messages.
When you switch logs all private strands have to be flushed to the current log before the switch is allowed to proceed.
So all in all this isn’t a bug or an error. As said above it’s similar to the “checkpoint not complete” message and can be also handled that way!